Sometimes it seems like politicians couldn't be more corrupt anyway, so will it make a big difference if corporations get to pump even more money into their campaigns? Probably yes; it will be interesting to see how that turns out.

Politically, it's one step further away from public campaign financing, which could produce a backlash sooner or later. Almost all significant actions provoke a reaction, so this decision is terrible, but it might at some point push reluctant idealists over the edge to reform campaign financing in a decisive way, in order to return to democracy as opposed to plutocracy.